116 THE DIATOMACE^E OF PHILADELPHIA AND VICINITY 



21. Spectabiles. Valve large, slightly arcuate, with excentric keel; no longitudinal 

 folds; keel puncta somewhat extended over the valve but much less than in the group 

 Insignes, and often scarcely perceptible. 



22. Lineares. Keel somewhat excentric, but less than in Spectabiles; frustule straight, 

 sometimes a little constricted in the middle, so that a transition is shown to the groups 

 Dubise and Bilobatae. Valve without longitudinal fold; keel puncta round or somewhat 

 angular, scarcely extended. 



23. Lanceolate. Valve lanceolate, linear-lanceolate or rarely elliptical, with very 

 excentric keel; not folded; keel puncta not extended. 



24. Nitzschiella. Valve with excentric keel and long, produced apices. 



TRYBLIOXELLA 



NITZSCHIA TRYBLIONELLA HANTZSCH 



Valve elliptical-lanceolate, with subacute apices; longitudinal fold well marked; striae 

 coarse, transverse, 5 in 10 n; indistinct puncta intermediate between the striae. L. 45 n. 

 Quite variable. 

 Blue clay. 

 PI. 32, Fig. 8. 



NITZSCHIA GRANULATA GRUN. 



Valve elliptical or elliptical-lanceolate; striae in double rows, each row of three or four 

 small puncta along the margin and rows of large puncta about 6 in 10 n across the valve. 

 L. 28-44 M . 



Blue clay. Along the coast. 



PI. 32, Fig. 3. 



NITZSCHIA NAVTCULARIS (BREB.) GRUN. 



Valve elliptical-lanceolate, with acute apices; striae on one side a double row of large 

 and small puncta, and on the other side radiate short rows of large puncta, 7 in 10 n; 

 middle of valve hyaline. L. 35-60 /n. 



Blue clay. Not common. 



PI. 32, Fig. 4. 



NITZSCHIA COMPRESSA (BAIL.) 



Valve elliptical-lanceolate, sometimes acuminate; striae, 6 or 7 in 10 n, coarsely 

 punctate. L. 56 //. 



Pyxidicula compressa Bailey. 



Nitzschia punctata (Wm. Sm.) Grun. 



Tryblionella punctata Wm. Sm. 



Common along the coast. 



PI. 39, Fig. 7. 



Var. minor (H. L. Smith). Valve acuminate; striae, 8 in 10 ft. L. 22 ft. 



Pyxidicula compressa var. minor H. L. Smith, Type Slide No. 431. 



PL 39, Fig. 8. 



The smaller forms occur northward, while the larger are found southward. This is 

 unquestionably Bailey's form, as indicated by his figure and by the fact that it is found 

 everywhere along the coast. Wm. Smith's T. punctata is the same species, although the 

 puncta are smaller. 



